Geography. Козлова Е.П. - 85 стр.

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                   17.1 The librarian who first measured the Earth

                                        Part I

      One morning the heralds spread the news through the town: King Ptolemy III
Evergetes had appointed Eratosthenes of Cyrene librarian of the great library of
Alexandria.
      Some people might have found it dull to be a librarian, but Eratosthenes was not
despondent. He decided to read everything he could find on travels and on
discoveries of the Earth’s secrets. Then he would write a big scientific book
containing all the geographical knowledge of those times.
      This work, which Eratosthenes called Geographica, took up a great deal of time.
Still sometimes the librarian would leave his quiet office and go out into the sunny
streets of the city. He would make his way to the Alexandrian bazaar where simple
folk argued and bargained.
      The royal librarian was wont to sit down somewhere in the shade of a shop wall
and start a conversation with the visiting merchants. One of them said: “ Our town of
Syene is the hottest place ever. They say there is no other such place on the sacred
Earth. Here when we sit in the shade it seems a bit cooler. But in Syene there is a day
once a year when there is no shade to be found . ”
      Eratosthenes was surprised.
      “ Wait, I don’t quite understand what you mean. A shadow may grow longer or
shorter, but I’ve never seen there to be none at all. ”
      “ Nevertheless, in our Syene, on June 22 at mid-day you will find no shade at
all, ” retorted the merchant stubbornly. “ Oh yes, on that day you can see the bottom
of the deepest and narrowest well. Believe me”.

                                          Part II

     The stranger’s story made Eratosthenes fall to thinking. He sought out and
reread manuscript after manuscript, trying to understand: “ How can such a thing be?
” It was the works of the great Aristotle that suggested the answer. That wise
philosopher asserted that the sun illuminates different parts of the Earth’s surface
differently and that its rays have different angles of incidence because the Earth is a
sphere; hence, the length of the sun's shade cannot be the same everywhere at the
same time.
     Now what if we turn to the Sun for help in measuring the size of the globe?
     That is just what the Alexandrian librarian decided to do. He had no intention of
making a long journey to measure the distance from one town to another step by step.
His idea was to measure the Earth without leaving the little courtyard of the
Alexandrian library. He constructed a special scatha or bowl, resembling a greatly
enlarged half nutshell. At the centre of the bowl he fixed a column. Then he set up his
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